The present invention relates generally to a cellular communications system including an airborne repeater, and particularly to techniques for locating system users within the system coverage area.
The increasing need for communications networks and capabilities in outlying and geographically diverse locations has created greater demand for cellular systems. Many new carriers providing the infrastructure for such systems have focused their resources on building as many terrestrial cell stations as possible to expand their respective areas of coverage and consequently generate more revenue.
However, the buildout rate for the terrestrial cell stations is typically slow and expensive, especially in mountainous or otherwise difficult to access areas. In addition, in some these areas, a carrier""s return on investment may not provide the incentive necessary for the carrier to build the necessary cell stations, thereby leaving these areas with either limited or no cellular service at all. Further, many areas having a sufficient number of cellular communications base transceiving stations to handle calls during both off-peak and peak times cannot adequately handle large volumes of calls during sporting events or other short-term special events that temporarily attract large crowds.
In response to the above, airborne cellular systems have been proposed in which a cellular repeater mounted in an airplane flying a predetermined flight pattern over a geographic area requiring cellular coverage links calls from cellular phones within the covered geographic area to a terrestrial base station. Because the airplane is capable of traversing geographic limitations and takes the place of the cell stations, such a system overcomes the above-mentioned limitations of conventional terrestrial cellular systems.
Despite its many advantages, an airborne cellular system presents design and implementation problems not present in the design and implementation of conventional terrestrial cellular systems. For example, service providers must be capable of accurately determining geographic locations of subscribers or roamers within their service areas for billing purposes, for example. In addition, real-time user location will be particularly important in next generation (2.5-3G) systems where data and multi-media services will be prevalent. Advertising will be a key operator revenue stream and location-based services/advertising will be premium. Because cell sites in conventional terrestrial cellular communications systems have very limited propagation ranges, subscriber and roamer locations can be determined rather easily with an accuracy corresponding to the limited ranges of the cell sites. However, because an airborne cellular communications system has a much wider propagation range, determining subscriber and roamer locations within the propagation range of the airborne cellular system presents unique challenges. In addition, accurate determination of geographic locations of subscribers or roamers within their service areas must become an essential feature of all cellular systems in response to a recent emergency 911 (E911) mandate requiring more precise system user location capabilities.